Number one check for the multiple areas of faults you will want to check the following:
I would start with system voltages and possible ingnition switch failure.
Keep in mind that a vehicle that has been in a mishap, can sometimes have a hidden problem which can take a highly skilled technician many hours to uncover with all of the correct diagnostic tools at his side along with the vehicle at his side. I will however do my best from here to help.
It would be helpful to know if there are any codes stored in any of the remaining many modules on the vehicle. Any "U" codes could show a splice pack that has been overlooked during a collision repair. Here's a diagram that ties many of your systems together that could be an area of concern.
As for the Code P0336 condition...this may or may not be related to the possible Ign. Switch problem you may be encountering. There is a very detailed set of diagnostics related to this stored code, and most of the concern points to your "Crankshaft Position Sensor" circuit problem.
DIAGNOSTIC AIDS DTC P0336 can be caused by secondary components leaking high voltage into the Ignition Control (IC) module. Inspect for the following conditions:
IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.
Have a qualified technician test the Ignition Switch for any voltage drop across it. Many times a portion of an Ignition switch that is failing, will allow just enough current to flow so that select system will not see enough system voltage to operate correctly. This may resolve many of your dash lamp concerns if found to have an Ign. switch failing.
I don't want to lead you in the wrong direction, but a I'm leaning toward a problem in the ignition switch.
You may have 2 distinct and isolated problems as I go through the your descriptions.
Start your diagnosis with being absolutly sure that your system voltages at fuse boxes downstream of the ignition switch.....voltages remain equal to the engine running system voltage that is measured at the battery. Both should remain up around 13.8v to 14.2v or so while the systems are under load. If you are seeing something say around 8 or 9 volts at the test points, then you'll want to replace the ginition switch.
A good place to make these voltage comparisons might be the PCM/ABS 10 A fuse. That would be the lower right fuse in the IP fuse panel
Although possibly not a swift and easy fix, I hope this information is helpful to you.
Have a Great Day
I have performed some hard troubleshooting in the past, so I`m not afraid of this one, I just wanted to put y effort on the right direction, since I`m not familiar with this particular GM product.I will be working on it during the upcoming weekend, following the instructions given.
I'll be away from my computer for the next 4 days during the daytime, however evenings and mornings I will check to see about any additional info you may need from me.